Problem With Ctrl C/V in Firefox after validating an input

[Guilherme Mendes]

Hello guys, I'm having some problems with Firefox for copy and paste via ctrl c/v after validating an input to get only numbers in it. I'm using the following code:function soNumero(event) { if (event.which) code = event.which; // Netscape 4.? else if (event.charCode) code = event.charCode; // Mozilla if((code < 48 || code > 57) && (event.keyCode != 8) //backspace && (event.keyCode != 9) //tab && (event.keyCode != 35) //end && (event.keyCode != 36) //home && (event.keyCode != 46) //delete && (code != 99) // ctrl + c && (code != 118) // ctrl + v && (event.keyCode != 37) && (event.keyCode != 39)) { // <- -> event.returnValue = false; return false; } }The function is called on an input at this way:<input id="txtNumeroCpfParam" class="entrada enabled2" value="0" onblur="javascript:tratarCpf(this.value);" onkeypress="return soNumero(event);" maxlength="11" size="12" name="txtNumeroCpf">The problem is: when I copy some numbers, e.g: 1234, and try to ctrl + v it on this input, nothing happens. The same when I have some numbers in the input and I try to ctrl + c. Anyone has an idea about how to proceed? This method works on Opera, without any changes. For other browsers I have another method, but I don't have any problems with them.
Sorry for english errors...